1. Field of the Invention
The present invention relates to an engine with horizontal cylinders, and more particularly to a lubricating oil passageway structure for an engine with horizontal cylinders and also to an outboard engine assembly which incorporates an engine with horizontal cylinders which has a lubricating oil passageway structure.
2. Description of the Prior Art
Engines with horizontal cylinders generally have lubricating oil supply and return passageways which interconnect a valve operating mechanism chamber defined between a cylinder head and a head cover, and an oil pan disposed in a lower portion of the engine.
Heretofore, as disclosed in Japanese Laid-Open Utility Model Publication No. 60-145209, the lubricating oil return passageway generally has an opening in a portion of the cylinder head which faces the bottom of the valve operating mechanism chamber, i.e., an inner bottom surface of the cylinder head which partly defines the valve operating mechanism chamber.
With the above disclosed lubricating oil return passageway, when the engine is tilted into a varied attitude, the distal ends of the horizontal cylinders may be displaced in a lower position, positioning the opening of the lubricating oil return passageway higher than the head cover portion that faces the bottom of the valve operating mechanism chamber. When such a positional displacement occurs, lubricating oil tends to remain trapped in the head cover portion lower than the opening of the lubricating oil return passage, and cannot fully be returned to the oil pan. Therefore, there has been a demand for an improvement in engines with horizontal cylinders to return the lubricating oil back to the oil pan.